Three years ago, at the age of 48, Camilla Rees had to leave her apartment in downtown San Francisco. Not because of the rent, she says, but because of the radiation.

Her personal radiation meter -- yes, such things exist -- spiked after a lawyer couple moved in next door. Rees asked the neighbors if they had installed a new Wi-Fi router, and sure enough they had, on the wall near Rees' bed. Rees says she quickly lost her ability to think clearly. "I was unfocused, as if I had suddenly come down with ADHD. I would wake up dizzy in the morning. I'd collapse to the floor. I had to leave to escape that nightmare."

Since then, Rees, a former investment banker, has been on a crusade against low-level electromagnetic fields, or EMFs, of all types, including the microwave radiation that flows from cellphones and cellphone towers and the magnetic forces surrounding power lines. She co-wrote the 2009 book "Public Health SOS: The Shadow Side of the Wireless Revolution," one of many recent books to warn against the dangers of EMFs, and founded the website electro magnetichealth.org.

"I'm one of the few people I know who has been able to recover from EMF," Rees says. "Other people are still suffering. They're disabled. I know people who have to live in trailers because the metal walls protect them."

Scientists can't agree on how electromagnetic fields might harm human health -- or even if there's any harm at all -- but that hasn't stopped waves of EMF panic from reaching new heights across the world, especially in Europe. The concern is building in this country too. U.S. activists and some researchers are loudly warning that electromagnetic pollution, or "electrosmog," is spreading death and disease, including cancer, infertility, Alzheimer's disease and autism. Last December, Rees and other activists led a panel discussion of the dangers of EMFs at Columbia Law School in New York City. An article in the February issue of GQ magazine suggests that cellphones are setting off a new worldwide epidemic of brain cancers.

Although the World Health Organization, the National Institutes of Health and many other major health organizations have officially declared that EMFs seem to pose little threat, governments are worrying too. Last April, the European Parliament passed a resolution (on a vote of 559 to 22) that called for countries to take major steps to reduce exposure to EMFs. Both San Francisco and Maine are currently considering requiring cancer warning labels on cellphones.

Widespread use

We live in a highly plugged-in world in which grade school students carry cellphones and adults move from one Wi-Fi hot spot to another. A recent survey from the Kaiser Family Foundation found that typical teens spend an hour and 20 minutes on a cellphone every day.

In the opinion of Ken Foster, a professor of bioengineering at the University of Pennsylvania in Philadelphia who has studied EMFs since the early 1970s, if such fields were any sort of health threat, scientists wouldn't have to sort through the outer limits of statistics to find trouble.

"There would be terrible effects all over the place," Foster says. As no obvious catastrophe has shown itself, "I would tend to think there's nothing there." (Keeping with the general tenor of the EMF debate, at least one researcher counters that Foster is "full of it" and "doesn't know what he's talking about.")

Dr. Martha Linet, chief of radiation epidemiology at the National Cancer Institute, has spent much of her career looking for any link between EMFs and cancer. She says studies so far suggest a weak connection, so weak that it might not exist at all.

She's now awaiting the final results of the Interphone study -- a large, multinational exploration specifically of cellphones and brain cancer partially funded by the European Union, partially by a cellphone industry group -- conducted in 13 countries outside the U.S. The final report should come out later this year, but data so far don't suggest a strong link between cellphone use and cancer risk, Linet says.

"I don't support warning labels for cellphones," Linet says. "We don't have the evidence that there's much danger. 'Don't use this while driving' -- now that's a warning I could get behind."

David Carpenter, who is a professor of environmental health sciences and biomedical sciences at the University at Albany, State University of New York, has analyzed the same studies that Linet and Foster have analyzed, but he's reached a very different conclusion. (For a closer look at these studies, see the related story.) Carpenter estimates that there's a greater than 95% chance that power lines can cause childhood leukemia and a greater than 90% chance that cellphones can cause brain tumors.

"It's apparent now that there's a real risk," Carpenter says. "The evidence is growing stronger every day."

In scientific circles, Carpenter is one of the loudest voices sounding the alarm against EMFs. He has written numerous scientific articles on the subject, and he was one of the contributors to the BioInitiative Report, a 2007 document that outlined theoretical dangers from EMFs and called for new safety standards for power lines and cellphone emissions.

Weak energy

There's one overriding reason why the scientific community at large isn't especially worried about low-level EMFs: To the minds of many, it's not physically possible for the small amounts of energy flowing from cellphones, Wi-Fi routers or power lines to have any effect on the human body.

Robert Park, professor emeritus of physics at the University of Maryland and author of "Voodoo Science: The Road From Foolishness to Fraud," published in 2000, literally laughs at the idea. "I don't understand how anyone with a knowledge of science could believe this stuff. I'm troubled that there's still such a deep division" among scientists.

It's true that cellphones and cellphone towers emit microwaves, which can sound scary to anyone who has ever burned something in a microwave oven. But microwaves have relatively long wavelengths -- and thus little energy. A light wave coming from a desk lamp has more energy than a microwave coming from a cellphone.

According to Park, these microwaves aren't nearly powerful enough to break apart DNA, which is how known threats such as UV rays and X-rays cause cancer. As long as a person doesn't absorb enough microwaves to actually cook themselves, he says, the energy would be far too feeble to do any damage.

Further, the fields around power lines (often called extremely low frequency, or ELF, fields) are much less powerful than the radiation from cellphones, Park adds, making any threats from power lines that much less plausible.

Lab studies have shown that rats and other animals can live quite happily in EMFs much stronger than any plugged-in, BlackBerry-toting human would ever experience. But such studies offer no comfort to Carpenter. "We're not concerned about the health of rats," he says. "We're concerned about the health of people."

Free radicals

Carpenter agrees that low-level EMFs aren't nearly powerful enough to directly break apart DNA. But he points out that many cancers are still poorly understood, and he strongly believes that low-level EMFs have enough power to cause mischief. "The evidence that some cells respond to electrical fields is overwhelming," he says. "Anybody who knows anything about biology knows that they can have an effect."

One possible scenario, according to Carpenter, is that low-level EMFs can encourage production of free radicals, destructive molecules that can damage cells and perhaps even break up DNA. It's already well-known that ultraviolet rays can create free radicals, and some laboratory studies suggest that low-level EMFs can do the same.

In 2008, Ashok Agarwal, director of research at the Center for Reproductive Medicine at the Cleveland Clinic, published a study showing that men who spent a lot of time on cellphones tended to have unusually low sperm counts. He has also conducted laboratory studies showing that cellphone radiation could damage sperm in test tubes.

Agarwal says there's not enough evidence to tell men with fertility problems to give up their cellphones, although he personally believes that spending 10 hours a day on the phone isn't exactly a fertility-friendly lifestyle, radiation or no. Men who want to protect themselves can simply put their cellphones in their shirt or jacket pocket instead of their pants pocket, he says. "It's a little inconvenient, but it might be safer."

Rees has her own defense strategy. She shuns cellphones and spends as much time as she can in low-EMF areas. "I like to spend time in the mountains and by the sea," she says. Getting far away from power lines and Wi-Fi hot spots feels relaxing and rejuvenating, she says.

Undoubtedly, that's true. But does her health -- or anyone's -- have anything to do with EMFs? That argument isn't over.